"We don't fully understand their nature or origin," astronomer Doug Finkbeiner of Harvard University said in a press release Nov. 9.

One prime suspect for the bubbles' creator is the supermassive black hole at the center of the galaxy, according to the study, published on arXiv.org and accepted to The Astrophysical Journal. Weighing in at more than 4 million times the mass of the sun, such a black hole is capable of furious outbursts of energy when surrounding matter falls into it.

"Another possible source of dramatic energy injection is a powerful starburst in the nucleus," Finkbeiner and other authors wrote in the study. Such a starburst is "driven by the energy released by supernova explosions and stellar winds following an intense episode of star formation," they wrote, and may have occurred some 10 million years ago.

Whatever is blowing the bubbles from the Milky Way’s core, the authors suspect new instruments, including the Planck spacecraft (launched in 2009) and the eROSITA X-ray telescope (scheduled to launch in 2012), will find out.

Images: 1) In this illustration, gamma-ray bubbles (purple) flanked by X-rays (blue) protrude 25,000 light-years each out of the Milky Way. NASA Goddard (hi-res). 2) The gamma-ray sky, as seen by NASA's Fermi space telescope. A dumbbell-shaped feature (yellow/orange) can be seen at galactic center extending out of the Milky Way's flat plane. NASA/DOE/Fermi LAT/D. Finkbeiner et al. (hi-res)**